Updated RenderTask test cases

Updated RenderTask test cases

Removed 2 test cases for a feature that is neither desirable or practical ( setting
the render task frequency to anything higher than 1 does not actually make the
update/render cycle at that frequency if nothing changes )

API description has been changed to reflect the current behaviour.

Fixed broken test cases, also found 1 actual error:

A resource response of LoadFailed doesn't make the UpdateManager
update the scene, whereas it should to ensure that attachments are correctly
set as completed status = NEVER; and for any dependent frame buffers to
be marked appropriately as well.

The 2 outstanding errors may also be real errors (in UtcDaliRenderTaskOnce03,
the scene graph gets drawn after the GL Sync occurs for no good reason; in
UtcDaliRenderTaskOnce08, no signal is sent ) but require further investigation.

Change-Id: I2ac9fd6dff68d4861ce1df9bbdc4d1dfb284b78d
Signed-off-by: David Steele <david.steele@partner.samsung.com>